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154 Posts
Discussion Starter #1 (Edited)
My Caliber has persistent overheating issues.

The car starts out running coolant temps at 210F and holds that for hours. After about four hours in 105F heat with a road surface at 150F, hitting 100+MPH once every 3 minutes (once per lap) and an average speed of about 60MPH or so, temps start to spike to 230F and more. When we bring it in, I find that we have lost almost a gallon of coolant.

I cannot replicate the issue under normal driving conditions.

I've detailed all my changes to attempt to fix this issue below. I will test to see if these changes have fixed my overheating issues on Feb 12. Let me know at least a week or two before then if you have other ideas for me to address this issue.

I've run a compression test, a cooling system pressure test, both of which came back fine. I run water only (this is mandatory). I've done a radiator flush and changed the water at least 6 times now. I've replaced the fuel injectors and all the other sensors. I've put in a much larger radiator.

In the Caliber, the coolant travels from the bottom of the right side of the radiator, through coolant adapter on the right side of the block (facing the rear of the car), through the coolant return tube across the back of the block (and directly under the exhaust manifold!), into the water pump, into the engine on the left side, and then it comes back out of the engine on the right side and goes to the top of the radiator on the left.

My current working theory as to why my car is overheating is that A, the stock non-SRT4 coolant adapter has poor flow characteristics and the coolant return tube passes within a half inch of the exhaust manifold on the back of the engine. I take steps below to address both issues.

This thread details a series of changes I made to improve airflow through the radiator:

Today, I made even more changes:

1. New water pump
2. I added the Caliber SRT-4 coolant adapter
3. Extra heat shielding

New Water Pump
This was a pain in the ass. Here is my rough process:

1. Drain cooling system
2. Remove accessory belt
3. Remove coolant adapter
4. Unbolt and remove the coolant return tube from the water pump (with the water pump still attached to the engine)
5. Unbolt and remove (or at least move) the lower heat shield of the exhaust manifold
6. Unbolt and remove the water pump

Reverse process to reinstall. Water pump bolts need 12.5nm.

SRT-4 Coolant Adapter
Below you can see the SRT-4 coolant adapter on the left and the regular Caliber coolant adapter on the right.

The regular coolant adapter has the thermostat on the coolant input from the radiator! This is the very first car I've ever seen with this configuration. The SRT-4 unit has the thermostat on the output like every other car. Also, it is important to know that our cars have two thermostats and two separate coolant loops, one for the block and a separate one for the head. You can see the thermostat for the head in the right side of the image immediately below, this is a high temp thermostat, something like 220F. For the SRT-4, the replace the head thermostat with a restrictor plate. You can see that I've previously taken the guts out of my block thermostat on the right to mimick the SRT-4 configuration.

The SRT-4 coolant adapter has much better flow characteristics and is a direct bolt on, at least for my 2007 RT manual.



You can see above that I've already blocked off the heater ports on the SRT-4 coolant adapter as I won't be using that on my car anymore.

You can see in the image below that my stock coolant adapter shows bubbling at the point where it connects to the coolant return tube in the picture below. The is very close to the point where the coolant return tube is closest to the exhaust manifold. I believe the water is boiling at this point causing poor flow, pump cavitation and overheating.


Has anyone else seen the bubbling in the picture above in their coolant adapter?

Extra Heat Shielding
Because the coolant return tube passes so close to the exhaust manifold, I put in extra heat shielding and sensors to monitor the temperature.

First, I put extra shielding inside the existing lower exhaust manifold heat shield:


Next, temperature sensors on the coolant return tube:


I then wrapped the tube with cool tape (heat resistant tape):


The I wrapped the coolant return tube in more heat shield and secured it with hose clamps:


Finally, you can see the new water pump with the pimped out coolant return tube and heat shield:


I'm hopeful that all of these changes will solve my overheating issues.

I'll let you all know after 12 Feb.

148 Posts
Have you tried running on E-85? Cooler burn, more power, less mileage, will turn on your CEL (thinks it’s a lean burn).

What did you change concerning thus car before you started having this problem? Find the root cause.

154 Posts
Discussion Starter #3
Have you tried running on E-85? Cooler burn, more power, less mileage, will turn on your CEL (thinks it’s a lean burn).
Wish I could run E85, I can't get it in the locations I need it.

I run 91 with 50ml of octane boost per gallon.

What did you change concerning thus car before you started having this problem? Find the root cause.
This is a good question. This car exhibited the problem on our first test. The engine is completely stock, and nothing appears to be blocked.

I believe a factory fresh Caliber would exhibit the same problems I'm seeing now.

Also, I should mention that I have been unable to replicate this issue on normal roads.
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